1. Field of the Invention
The present invention relates to an at least partially implantable hearing aid and a corresponding method for providing hearing assistance to a patient.
2. Description of Related Art
Implantable middle ear hearing devices (IMEHD) are offered for people with special hearing losses or special medical indications which cannot be treated with conventional electro-acoustic hearing aids. Typical indications for IMEHDs are radical middle ear cavities, atresia and otosclerosis (especially in combination with sensorineural hearing loss) and chronic infects or allergies of the ear canal.
All IMEHDs have in common that they bridge the non-functioning sound path of the middle ear ossicles by directly mechanically stimulating the cochlear. For this stimulation, various types of actuators have been proposed (e.g., piezoelectric or electro-magnetic) and several are available in certified medical products. All of these actuators have in common that they are placed somewhere in the middle ear cavity. In order to deliver the sound vibration to the cochlear fluids, they are coupled, in most cases, either (a) to the ossicular chain or (b) to the Round Window, or (c) to a piston placed in a small hole drilled in the cochlear in or close to the stapes footplate. Most of these actuator principles need a rigid fixation of the actuator housing on the bone.
For people suffering from deafness or partial deafness, Cochlear Implants (CI) are offered. These devices bypass the outer and the middle ear and stimulate the auditory nerve electrically with an electrode-chain inserted in the cochlea. For people with residual hearing, mostly in the low frequency range, it was shown that, in addition to the electrical stimulation, acoustical stimulation at the frequencies with residual hearing can be beneficial for speech understanding, sound quality and music perception. In today's hybrid systems, the acoustic amplification is realized by integrating an amplifier and a receiver in the CI speech processor and delivering the amplified sound through a tube and a custom-made ear mold to the ear canal as done with conventional hearing aids. The receiver can also be integrated in the ear mold.
Implanting the fixation system of the IMEHD actuator increases the invasiveness and duration of the surgery, which means a higher risk for the patient. However, the major issue is that the precise mechanical adjustment of the actuator in the fixation system and the proper connection to the ossicles, the round window or the piston is the most difficult part of the surgery. Bad fixations or couplings can lead to significant loss of vibration energy and distortions, so that the stimulation arriving at the cochlear fluids is not sufficient to re-establish normal hearing, or even to provide the amplification necessary to compensate a sensorineural hearing loss.
Also, for actuator principles without a fixation system, the risk of inefficient vibration transmission to the inner ear exists. For example, a Floating-Mass-Transducer (FMT) which is directly crimped on the incus needs proper alignment and can become less efficient if the motility of the ossicular chain is reduced. The crimping can also cause inflammatory reactions of the ossicles.
International Patent Application Publication WO 2008/077943 A2 and corresponding U.S. Patent Application Publication 2010/0324355 relate to a hearing aid comprising an actuator having a membrane with a piezoelectric disc-bender arrangement for directly vibrating the inner ear fluids in the cochlear. The membrane is located in a frame structure outside the cochlear, with an open end of the frame being inserted into an opening in the cochlear wall.
International Patent Application Publication WO 03/063542 A2 and corresponding U.S. Pat. No. 7,289,639 relate to a hearing aid comprising an actuator which is a thin disc made of piezo-ceramic material, such as PZT (Lead Zirconate Titanate), which drives, via a fluid-filled tube, a larger diameter disc actuator which contacts the perilymph, wherein the actuator is located outside the cochlea.
U.S. Patent Application Publication 2006/0161255 A1 and corresponding U.S. Pat. No. 7,618,450 B2 relate to a hearing aid comprising a bone-mounted piezoelectric actuator which drives a membrane in contact with the perilymph.
German Patent Application DE 10 2007 026 631 A1 relates to an actuator for a hearing aid inserted into the cochlea, comprising electrodes and electro-mechanical transducers which are implemented as piezoelectric elements.
U.S. Pat. No. 6,565,503 B2 relates to a hearing aid including an actuator to be inserted into the cochlea, which comprises a combination of cochlear implant electrodes and piezoelectric transducers.
U.S. Pat. No. 6,549,814 B1 relates to a hearing aid comprising a cochlear electrode array, which is inserted underneath the spiral ligament of the lateral wall of the cochlear without penetrating into the cochlea. The electrode array may include mechanical transducers implemented as a piezoelectric film.
U.S. Patent Application 2005/0177204 A1 and corresponding U.S. Pat. No. 7,580,754 B2 relate to a piezoelectric pressure sensor which is inserted into the cochlear in direct contact with the perilymph for acting as a microphone.